Reconstruction techniques for determining O/F in hybrid rockets

In this study, the accuracy of reconstruction techniques for determining instantaneous O/F (oxidizer to fuel mass ratio) is investigated using numerical firing tests for which O/F and η_c∗ (efficiency of characteristic exhaust velocity, c^∗) are known. Six methods are introduced and compared: OPMA-F-C (constant c^∗), OPMA-F-E (constant η_c∗), OPMA-F-CE (to avoid the multiple solutions problem), OPTMA-FE-L (constant thrust coefficient, λ), OPMA-F-CE (modified CEA), and OPTMA-FE-L (modified CEA). The calculation results show the advantages and disadvantages for each method in cases of noisy data, multiple solutions problem, and O/F and η_c∗ shifts. For the multiple solutions problem, the OPMA-F-CE method is recommenced for the O/F and η_c∗ calculations. In the case of the O/F shift, the OPMA-F-E, OPTMA-FE-L, OPMA-F-E (modified CEA), and OPTMA-FE-L (modified CEA) methods are recommenced for the O/F and η_c∗calculations, however, when the O/F is shifting within the multiple solutions range, an accurate O/F result is not obtained by any of the methods in this study. In the case of the η_c∗ shift, the OPTMA-FE-L and OPTMA-FE-L (modified CEA) methods are recommended because η_c∗ is not constant in these methods. However, in the case where η_c∗ and O/F shifts occur and there is noise in the multiple solutions range, an accurate O/F cannot be obtained by any of the methods.